Transmission of petroleum products through a frozen medium

ABSTRACT

A method and apparatus for transmitting petroleum and like products generally horizontally through a frozen medium in which the more viscous oil, pumped at higher temperature, is transmitted through an inner conduit, and liquified natural gas or other suitable refrigerant medium is transmitted in an outer coaxially-disposed annular conduit insulated from the inner conduit, the refrigerant medium being held in a constant physical state. The surrounding permafrost is stabilized by the refrigerant medium.

United States Patent [191 Lefever TRANSMISSION OF PETROLEUM PRODUCTS THROUGH A FROZEN MEDIUM Inventor: Kenneth W. Lefever, Waterford, Va.

Filed: Oct. 9, 1973 Appl. No.: 404,624

Related U.S. Application Data Continuation of Ser. No. 124,065, March 15, 1971, abandoned.

U.S. Cl 137/13, 62/260, 165/45, 166/DIG. 1

Int. Cl. F17d 1/16 Field of Search 62/55, 260; 137/13; 165/45; 166/DIG. 1

References Cited UNITED STATES PATENTS 3/1972 Burnside l66/DIG. l

Primary Examiner-Meyer Perlin Assistant Examiner-Ronald C. Capossela Attorney, Agent, or Firm-Bacon & Thomas [57] ABSTRACT A method and apparatus for transmitting petroleum and like products generally horizontally through a frozen medium in which the more viscous oil, pumped at higher temperature, is transmitted through an inner conduit, and liquified natural gas or other suitable refrigerant medium is transmitted in an outer coaxiallydisposed annular conduit insulated from the inner conduit, the refrigerant medium being held in a constant physical state. The surrounding permafrost is stabilized by the refrigerant medium.

4 Claims, 6 Drawing Figures 1 TRANSMISSION OF PETROLEUM PRODUCTS THROUGH A FROZEN MEDIUM This application is a continuation of copending US. application Ser. No. 124,065, filed Mar. 15, 1971 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the transportation of materials by a generally horizontal pipeline, and more particularly to the transportation of petroleum products by a generally horizontal pipeline from the fields in the North Arctic Slopes through the permafrost layer to the south.

2. Description of the Prior Art A principal problem encountered in any construction in or through permafrost is the instability of composition. Permafrost is a ground layer prevalent in arctic and antarctic regions which is a mixture of earth and frozen water resulting from the prevailing ambient temperatures. During the arctic summer the permafrost in some areas thaws to some degree for depth varying from six inches to two feet. These areas when thawed become quite unstable, and incapable of supporting normal structures.

In the transmission of oil from the oil fields on the North Arctic Slopes, the oil is extracted from the ground above 140 F., and this temperature or at least an elevated temperature that will assure free flowing of the oil is maintained during transmission by energy imparted by the pumping stations along the line. Precooling of the oil is not accomplished because the viscosity thereof would be increased, thereby rendering transmission more difficult. The pipeline therefore becomes a heat source and itself becomes a de-stabilizing factor in placing a pipeline in the permafrost.

Various means have been proposed for overcoming the above problems, one of which is elevation of the pipeline above the permafrost on platforms. This method, although avoiding direct thawing of the permafrost, has several disadvantages, not the least of which is the widespread opposition by the public to the bisection of large areas of the Northland by such a physical barrier, with the attendant effect on the environment. Other disadvantages are that the exposed pipeline is vulnerable to damage by natural or manmade forces, thereby providing an ever-present threat to the environment. Furthermore, within the state of the art, it is difficult to prevent transmission of heat from the pipeline through the supports, thereby rendering the permafrost liable to instability through thawing.

permafrost in a frozen condition. A rather unique trench structure is required for the two pipelines, making contruction somewhat difficult and expensive. More importantly, the use of a separate pipeline for the refrigerant tends to concentrate the freezing effect on the permafrost over but a single side of the trench and the hot petroleum transmission pipeline, and thus an even freezing effect on the permafrost completely about the hot pipeline is not assured.

In US. Pat. No. 3,674,086, directed mainly to the maintenance of permafrost in a frozen condition about a vertical well head pipe, another approach to the problem of horizontal transmission is presented. In the patent a pair of concentrically disposed pipelines is provided, with hot petroleum being transmitted through the inner pipe, and a refrigerated medium through the outer pipe. Insulation is provided on the exterior of the outer pipe, which has the adverse effect of limiting the effect of the refrigerated medium on the permafrost. More seriously, no insulation is provided on the inner pipe, with the result that over any substantial length of pipeline the refrigerated medium will soon cool the hot petroleum to the point where it will stiffen, and fiow will be slowed or halted. Further, when the refrigerant is LNG or the like, the possibility exists with this arrangement that the LNG will be gassified with a tremendous increase in pressure, possibly causing a blowout of the pipeline. The approaches in both of these patents thus fail to fully solve the problems of transmitting hot petroleum generally horizontally through permafrost without destroying the frozen permafrost itself, for the reasons given, and further because they ignore other difficulties inherent from the undulating terrain over which such a pipline must pass.

It should also be noted that, as in US. Pat. No. 3,674,086 just mentioned, there have been proposals for transmitting hot petroleum vertically, as opposed to horizontally, through a permafrost layer. Two further patents showing such arrangements are US. Pat. Nos. 3,613,792 and 3,650,327. The arrangements of all three patents are designed to maintain permafrost in a frozen condition during the transmission of hot petroleum vertically therethrough, and make use of an outer conduit concentrically disposed about an inner conduit through which the petroleum is transmitted, a refrigerant being disposed in the outer conduit. The vertical arrangements of the three patents cannot be used with complete success in a horizontal pipeline, however, because of inherent unique difficulties found in such a horizontal pipeline.

There is thus no present method known to the applicant that is fully satisfactory for transmitting hot petroleum generally horizontally for long distances through arctic permafrost, designed to maintain the permafrost in a frozen condition. There is need for such a method, one that will work in undulating terrain over long distances, that will not retard the flow of the petroleum, and which will assure even freezing of the permafrost on all sides of a pipeline transmitting the hot petroleum. The present invention is intended to satisfy that need.

SUMMARY OF THE lNVENTlON This invention provides a method for stabilizing arctic permafrost to enable transmission of petroleum products by pipeline therethrough.

The invention further provides a means to stabilize permafrost around a pipeline by refrigeration derived from compression of one of the petroleum products, or some other suitable refrigerant medium, transmitted through the pipeline.

In a preferred embodiment, this invention provides a method of ,stabilizing permafrost around a petroleum product transmitting pipeline, comprising the steps of:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is partly a schematic elevational view of a pipeline in accordance with the invention;

FIG. 2 is an enlarged sectional view of the embodiment of FIG. 1, taken along the lines 2-2 thereof;

FIG. 3 is a broken, axial view of a second, two-pipe embodiment of the pipeline;

FIG. 4 is a sectional view taken on the line 44 of FIG. 3;

FIG. 5 is a graph showing the temperature of the refrigerant medium versus pipeline length for a specific example of a pipeline made according to the invention; and

FIG. 6 is a diagramatic representation showing the pipeline of the invention installed over undulating terrain, indicating how a mixed gaseous and liquid state for the refrigerant medium can create a block to the transmission of the refrigerant medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2 of the drawings, the pipeline, shown generally at 10, comprises an inner conduit 12, an intermediate conduit 14 and an outer conduit 16 buried in permafrost 18.

The inner conduit 12 and the intermediate conduit 14 areprovided with radially-extending struts 20 provided on their outer ends with friction-reducing shoes or rollers 22 which engage the inner surface of the next succeeding conduit and provide spaced support between the conduits such that an inner space 24, an intermediate annular space 26, and an outer annular space 28 are formed thereby.

The pipeline is provided at the source end with a means for providing separate communication with the various spaces 24, 26 and 28 within the line. The means consists, in the illustrated embodiment, of a head 30 through which the inner conduit 12 passes to communicate with a source of oil (not shown). The intermediate conduit 14 terminates within the head and has communicating, therewith a branch pipe 32 and pump 34, which communicate with a source of material to be described below. The outer conduit 16 communicates with a branch pipe 36 and a pump 38, which in turn communicates with a source of refrigerant medium, such as liquifred natural gas (not shown).

In operation, the above described system is connected to a source of crude oil through conduit 12 for transmission in the pipeline 10, so that the inner space 24 is filled with crude oil preferably pumped at a temperature of about 140 F, as is known in the art. Assuming the use of natural gas as a refrigerant medium, such is preferably derived from the same source as the crude oil, is liquified by means known in the art (now shown) and is then pumped into the outer conduit 16 through the pipe 36 to thereby fill the outer space 28 throughof the transmission pipe segment, for reasons that will be explained later. Pumping stations are provided at suitable intervals along the length of the pipeline to boost the pressure of the fluid and maintain liquidity thereof. If a gaseous refrigerant medium is employed, it is pumped and handled so as to remain in its gaseous physical state.

The intermediate space 26 serves as a buffer or insulation between the outer space 26 and the inner space 24 so that the oil in the latter is not quickly cooled by the fluid in the former, or vice-versa. In the absence of such insulation, over a prolonged distance the refrigerant medium can so cool down the hot petroleum as to cause a stiffening thereof that will slow or stop flow. Thus, such insulation is essential to the successful operation of the subject pipeline. This insulation space may also serve to transmit other materials to or from the oil field site, which materials further serve to provide a buffer or balance between the temperatures of the oil and fluid in the outer space 28.

The fluid in the intermediate space 26 can be selected to aid, in the event of a pipeline break, in the freezing of the oil from the inner conduit 12, and thereby shut off flow to prevent spillage of oil to the surrounding terrain. This feature is not obtainable in separate pipe arrangements like that in US. Pat. No. 3,650,119, mentioned earlier, and is important to protection of the environment. The selected fluid could be, for example, an oil sorbent material which would operate to absorb oil upon a break to further inhibit the flow of oil from the break. The sorbent material must be water repellant such that water is not absorbed. A material suitable for the purpose is an expanded perliteasphalt-fiber compound marketed under the trademark Sorbent C by Clean Water, Inc. of Toms River, New Jersey.

The transmission of the refrigerant medium within the pipeline provides additional benefits other than those set forth above in that the fluid may be utilized to maintain year-round stability in the permafrost above or adjacent the pipeline to provide an access road therefore, and to stabilize adjacent facilities such as pumping and compressing stations and the like. When liquified natural gas (LNG) or liquified propane gas (LPG) are used as the refrigerant medium, such can also provide fuel for operating the pumping and compression stations as well as a source of heat for maintaining or raising the temperature of the oil.

The materials utilized to construct the conduits 12, 14 and 16 of FIGS. 1 and 2 are of course a matter of choice, it being contemplated that the inner and intermediate conduits 12 and 14 would normally be of steel, whereas the outer conduit 16 might be of steel or reinforced concrete. The use of reinforced concrete for the outer conduit can offer great economies, in that such can usually be produced nearby, whereas large diameter steel pipe must be fabricated and transported very long distances to be used in the arctic or antarctic regrons.

It is also contemplated that the buffer or insulation 26 formed between the inner conduit 12 and the outer annular flow space 20 might be obtained in other ways than by utilizing three concentrically spaced conduits. For example, only two conduits might be utilized, with the inner conduit carrying a jacket of insulative material with buffering or insulative qualities similar to those offered by the annular intermediate space 26 between the conduits 12 and 14. Because such a two-pipe arrangement would eliminate the fabrication, transportation and installation costs of the intermediate conduit 14, it should be more economical to construct than the three-pipe arrangement of FIGS. 1 and 2. At the same time, however, the opportunity to transmit a third substance through the intermediate space 26 would be absent in a two-pipe system.

Referring now to FIGS. 3 and 4, a two-pipe embodiment of the invention is shown at 50 installed in permafrost 52, the pipeline 50 including an inner conduit 54 of steel or a similar material, and an outer conduit 56 made of reinforced concrete. The inner conduit 54 would normally be made of pipe sections welded into a continuous conduit, whereas the outer conduit 56 would consist of reinforced concrete pipe sections 58 joined by suitable socket joints 60 each having a relatively high pressure gas-tight seal 62.

The inner conduit 54 is supported concentrically within the outer conduit 56 by radially-extending struts 64 similar to the struts 20, and has a jacket 66 of insulative material wrapped thereabout to form a buffer or heat exhange interface between the flow space 68 within the inner conduit 54 and the annular outer flow space 70 between the conduits 54 and 56. The jacket 66 can be of any suitable construction and materials, but as shown in FIGS. 3 and 4 constitutes an axially split styrofoam sleeve 72 wrapped with the same kind of reinforced paper 74 that is normally used in pipeline construction.

The two-pipe 50 pipeline of FIGS. 3 and 4 is used to transport petroleum in a manner like that for the pipeline 10, the heated petroleum being transmitted through the inner flow space 68, and a cold refrigerant medium being transmitted through the outer annular flow space 70. The pipeline 50 can be of any length up to several hundred miles and beyond, and is provided periodically with booster pumping stations (not shown) for the petroleum, and compressor stations (not shown) designed to recharge and restore the refrigerant medium, it being remembered that the medium according to the invention must remain in a constant physical state. Typically, the pumping and compressor stations would be 50 to 80 miles apart.

The particular refrigerant medium chosen for use in the systems of either FIGS. 1 and 2 or FIGS. 3 and 4 is a matter of choice based upon many factors. In addition to LNG and LPG, methane and the more conventional mediums can be employed, the medium acting as a moving heat sink to accept and hold heat from the hot petroleum flowing through the inner pipe, and never being allowed to reach a temperature such as would resuit in melting of the permafrost. The flowing refrigerant medium enters the outer annular flow space at a first, cold temperature, is warmed through heat transfers and friction as it flows, and is removed from the flow space before it reaches 32 F at a compressor station. The excess heat is removed from the medium at the station, and the recharged medium is then pumped back into the pipeline to again act as a moving heat sink.

There are many factors that must be taken into account in an actual pipeline, and which affect and are affected by the materials of construction, the pipeline dimensions, the selected refrigerant medium, and the heated fluid to be transported. For the purpose solely of illustrating the factors involved in a typical installation, and not by way of limitation, the following example for a typical installation is provided.

EXAMPLE:

For purposes of this Example a two-pipe pipeline similar to that of FIGS. 3 and 4 is buried at an average centerline depth of six feet below the summertime permafrost thaw line, the inner conduit having an inner diameter of 48 inches and carrying an insulation jacket thereon, and the outer conduit having an inside diameter of 72 inches.

The overall length of the pipeline of the Example is about 850 miles, with oil pumping and refrigerant compressor stations to be at least every miles. The material to be transported is crude oil at an initial temperature of F and at the flow rate of 2 X 10 barrels per day, and the refrigerant medium is methane transported through the outer annular space at a flow rate of about 2 X 10 standard cubic feet per day. The pressure drop in the inner conduit would be about 12 psi per mile, and for purposes of calculation a level pipeline section is assumed.

The insulation jacket on the inner pipe is chosen to have heat conductivity about as follows in Equation l, and the conductivity of the permafrost is assumed to be about as in Equation 2:

Equation 1 0.01 BTU/hr-ft-F (2.78 X 10 BTU/S-ft-F) Equation 2 1.28 BTU/hr-ft-F (3.55.8 X 10 BTU/S-ft-F) FIG. 5 of the drawings illustrates graphically the results derived from a mathematical model of the pipeline system described in this Example, and indicates that if the initial temperature of the methane refrigerant medium at the beginning of each 100 mile pipeline segment is held below l5 F, the final temperature of the medium at the end of the 100 miles will not exceed 30 F, insuring that the permafrost will not be thawed. If the oil pumping and refrigerant compressor stations are spaced closer than 100 miles apart, then even better results can be obtained. For reasons of power requirements and a safety factor to prevent thawing of the permafrost, and to reduce the pressures required in the refrigerated gas heat sink, a station spacing of about 50 to 80 miles is preferable for the system as described.

If the traveling heat sink formed by the refrigerant medium is to be effective, then the medium must flow continuously through the pipeline, preferably in the same direction as the hot petroleum. In order for such flow of the refrigerant to be assured, the physical state thereof should remain the same at all times. That is, if a liquid refrigerant is used, it should remain a liquid, and a gaseous refrigerant should remain a gas. The medium must be placed under adequate pressure to ensure this steady physical state, and the compressor stations are so located as to take this need into account.

The reason why it is undersireable to mix liquid and gas in the refrigerant pipeline is that the liquid may create a blockage, in the presence of the usual vertically undulating terrain over which a pipeline is laid. Referring now to FIG. 6, a pipeline 50 is shown installed over a many mile length, with the terrain undulating, as is usually the case. The vertically undulating terrain will often cause high and low points in the pipeline, and if a mixed liquid and gas is used as the refrigerant me- .dium, the liquid can gather in a low point as shown in I FIG. 6, and thereby block refrigerant flow. Should this occur, then obviously the effectiveness of the present method would be impaired.

If the refrigerant is a liquid and under a suitable constant pressure, then the refrigerant conduit will be filled, and such blockages because of vapor accumulating at high points in the undulating pipeline cannot occur. Similarly, if liquification is prevented when the refrigerant is all in a gaseous state, then liquid blocks cannot be formed by accumulations of liquid at low points in the undulating pipeline. But the mixed physical states of liquid and gas can cause problems from vapor and liquid blocks, and should be avoided if an efiective pipeline arrangement is to result.

It is thus seen that in the method of the invention there has been provided a manner for efficiently transmitting hot petroleum through frozen permafrost, in such a manner that the permafrost will remain frozen. The difficulties of past proposals for such transmission have been overcome, and a workable system is the result. Obviously, many modifications and variations of the invention are possible.

I claim:

1. The method of transmitting a petroleum product generally horizontally through a frozen medium which is structurally unstable at temperatures at or above 32 F., comprising the steps of: transmitting said petroleum product in a liquid state at a temperature in excess of 32 F. through a generally horizontal inner conduit disposed in said frozen medium; and simultaneously transmitting a refrigerated medium held at a temperature substantially below 32 F. and under continuous pressure through an outer annular conduit disposed in spaced coaxial relation to said generally horizontal inner conduit to maintain said frozen medium in a stable state, said outer coaxially disposed conduit being insulated from said generally horizontal inner conduit whereby said petroleum product is not changed from a liquid state to a stiff or solid state by said refrigerated medium, and said refrigerated medium being maintained in a steady single physical state during transmission therof to enable uninterrupted transmission over long distances in a generally horizontal but vertically undulating pipeline.

2. The method of claim 1, wherein only two conduits are employed, the inner of said conduits having insulation mounted thereon.

3. The method of claim 1, wherein an intermediate conduit is concentrally disposed in spaced relationship between said outer conduit and said inner conduit, the

space between said inner and said intermediate conduits containing an intermediate fluid which is transmitted through said space to provide a temperature balance therebetween, whereby to help establish said insulation.

4. The method of claim 3, wherein said intermediate fluid contains an oil absorbent fluid slurry. 

1. The method of transmitting a petroleum product generally horizontally through a frozen medium which is structurally unstable at temperatures at or above 32* F., comprising the steps of: transmitting said petroleum product in a liquid state at a temperature in excess of 32* F. through a generally horizontal inner conduit disposed in said frozen medium; and simultaneously transmitting a refrigerated medium held at a temperature substantially below 32* F. and under continuous pressure through an outer annular conduit disposed in spaced coaxial relation to said generally horizontal inner conduit to maintain said frozen medium in a stable state, said outer coaxially disposed conduit being insulated from said generally horizontal inner conduit whereby said petroleum product is not changed from a liquid state to a stiff or solid state by said refrigerated medium, and said refrigerated medium being maintained in a steady single physical state during transmission therof to enable uninterrupted transmission over long distances in a generally horizontal but vertically undulating pipeline.
 2. The method of claim 1, wherein only two conduits are employed, the inner of said conduits having insulation mounted thereon.
 3. The method of claim 1, wherein an intermediate conduit is concentrally disposed in spaced relationship between said outer conduit and said inner conduit, the space between said inner and said intermediate conduits containing an intermediate fluid which is transmitted through said space to provide a temperature balance therebetween, whereby to help establish said insulation.
 4. The method of claim 3, wherein said intermediate fluid contains an oil absorbent fluid slurry. 